Exposed lens plate luminaires typically comprise LED modules mounted in a housing or supporting mechanism with no additional shielding or protection provided to the light emitting surface of the LED module. As such, an exposed lens plate luminaire may have fewer parts than other lighting arrangements, resulting in a lower cost luminaire with increased light output and an improved beam profile.
Known LED modules employed in exposed lens plate luminaires comprise an LED light source; and an optically transmissive cover element (hereinafter referred to as an optical cover plate). The LED light source typically comprises a printed circuit board (PCB) with a plurality of LEDs mounted thereon, said LEDs being adapted to output light from a light-emitting surface of the printed circuit board. Optionally, such LED modules are known to further comprise additional thermal management elements, e.g. a heat sink.
Employing an optical cover plate to cover the LEDs mounted on the PCB typically introduces optical losses in the region of 5-10%. Due to size and weight constraints for a luminaire, such losses cannot be compensated by installing more LEDs or driving them at a higher current.
Further, employing a single optical cover plate to cover a relatively large PCB is not feasible because large optical plates cannot be produced via injection molding. Also, large optical cover plates can introduce alignment problems between optical elements of the optical cover plate and the LEDs, due to tolerances, differences in thermal expansion, and/or stresses due to differences in thermal expansion.